While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF, ArF or F2 laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less. In these lithography processes, resist materials comprising various alkali-soluble resins as the base resin are used.
For resist materials for use in the KrF laser lithography, in fact, polyhydroxystyrene resins become the standard. For ArF resist materials, studies are made on poly(meth)acrylate resins utilizing carboxyl groups as the alkali soluble group and polymers of cycloaliphatic olefins such as norbornene. Of these, poly(meth)acrylate resins are practically used because of ease of polymerization.
As for the poly(meth)acrylate, JP-A 9-90637 proposes a combination of methyladamantyl(meth)acrylate as acid labile group-containing recurring units with lactone ring-containing (meth)acrylate as adhesive group-containing recurring units. JP-A 2000-327633 discloses an acid labile group having an exo-isomer of a tertiary alkyl group of alkylbicyclo[2.2.1]heptanol form. This acid labile group is easily acid eliminatable, requires only low activation energy for acid elimination, and provides for a high resolution and less dependence on post-exposure baking (PEB). As the adhesive groups with enhanced etching resistance, JP-A 2000-26446 and JP-A 2000-159758 propose (meth)acrylate units having norbornane-lactone and oxanorbornane-lactone, respectively. These works resulted in ArF resist materials having significantly improved resolution. Also, JP-A 2003-113213 discloses a ternary polymer comprising acid labile group units, lactone units, and hydroxyl-containing recurring units as derived from 3-hydroxy-1-adamantyl(meth)acrylate, for controlling the diffusion within a resist film of the acid generated by the photoacid generator upon exposure. This polymer is also useful as a base resin in resist materials.
While the control of acid diffusion within resist film is indispensable to maintain various process margins, typically exposure latitude (EL) and mask error enhancement factor (MEEF), and to establish high resolution resists, the 3-hydroxy-1-adamantyl(meth)acrylate units have the drawbacks of lower resist sensitivity and pattern collapse due to excessive swelling. There is a desire to have novel acid diffusion control units.
Citation List                Patent Document 1: JP-A H09-90637        Patent Document 2: JP-A 2000-327633 (U.S. Pat. No. 6,448,420, EP 1053986B1)        Patent Document 3: JP-A 2000-26446        Patent Document 4: JP-A 2000-159758 (U.S. Pat. No. 6,280,898)        Patent Document 5: JP-A 2003-113213        